For example, as disclosed in PTLs 1 and 2, a known excavation tool includes those which form an excavation pit in the ground or in rock in the following manner. A steel tool body, to a distal end of which multiple excavation tips made of sintered alloys such as ultra-hard metal alloys are attached, is attached to a distal end portion of an excavation rod or is attached via a device to the distal end portion of the excavation rod. The excavation tool uses a rotating force about an axis line of the tool body, which is transmitted from an excavator via the excavation rod, a thrust force toward the distal end side in a direction of the axis line, and a striking force toward the distal end side in the direction of the axis line, which is transmitted from a down-the-hole hammer via the device in addition to the rotating force and the thrust force.
Incidentally, the excavation tool in the related art has a configuration as follows. In an embedding hole drilled in the distal end portion of the tool body, an excavation tip made of the sintered alloys is configured so that a cylindrical embedding portion is formed integrally with a spherical, conical or bullet-shaped cutting edge portion disposed in a distal end side of the embedding portion. The excavation tip protrudes the cutting edge portion from the embedding hole. The embedding portion is firmly fixed in the embedding hole by interference fit such as shrink fitting. In this manner, the embedding portion is embedded in and attached to the embedding hole.
Then, in this excavation tool used in excavating the ground or the rock, the cutting edge portion of the excavation tip which is protruded from the embedding hole in this way is used in excavating by being brought into contact with the ground or the rock and by being caused to penetrate the ground or the rock. Correspondingly, wear and abrasion of the cutting edge portion progressively occur. In the worn cutting edge portion, the radius of curvature increases on the curved surface thereof. Therefore, the sharpness of the cutting edge is impaired, thereby the excavation efficiency decreases. Furthermore, if the wear of the excavation tip progressively occurs until the diameter of the excavation pit becomes an acceptable diameter or smaller, the tool life of the excavation tool is finished.
However, the wear and the abrasion of the cutting edge portion of the excavation tip are not uniform. For example, among the multiple excavation tips embedded in the distal end portion of the tool body, especially in the excavation tip embedded in a gauge portion of an outer peripheral side of the distal end portion, the wear and the abrasion become significant on a surface facing the outer peripheral side. Since asymmetrical wear occurs, an excavation performance is likely to be impaired, thereby causing decreased excavation efficiency. This wear of the excavation tip in the gauge portion is relevant to a decrease in the diameter of the excavation pit, and thereby seriously affects tool life.
Then, this uneven wear of the cutting edge portion of the excavation tip is more significant under conditions where the cutting edge portion is seriously worn due to the hard ground or rock. As a result, the tool life is shortened and the cost for excavation increases. In addition, it also takes money and time to regrind the cutting edge portion of the excavation tip in order to recover the excavation performance. Furthermore, if the tool life of the excavation tool is finished before the excavation pit is excavated to reach a desired depth, it takes time, effort and money to replace the tool body. In addition, if the wear and the abrasion of the cutting edge portion progressively occur and yet the excavation is continued while the excavation performance remains impaired, the wear or damage may occur in the tool body, and an overload is imposed on the excavator.